Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 041457 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1058 AM EDT FRI SEP 4 2015 .SYNOPSIS...A BACKDOOR COLD FRONT WILL APPROACH FROM THE NORTH LATE TODAY...THEN PUSH SOUTHWARD THROUGH THE AREA TONIGHT...BEFORE SETTLING TO OUR SOUTH ON SATURDAY. HIGH PRESSURE WILL EXTEND INTO THE REGION FROM THE NORTH OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1058 AM FRIDAY... A WEAK COLD FRONT OVER THE MID-ATLANTIC STATES WILL DROP SOUTH INTO THE LATE THIS EVENING. MOISTURE FLUX CONVERGENCE ALONG THE FRONT COUPLED WITH WEAK SHORTWAVE IMPULSES EMBEDDED ON THE BACK SLIDE OF THE DEPARTING SHORTWAVE TROUGH OFF THE SOUTHEAST COAST WILL SUPPORT SCATTERED SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND THROUGH THE EVENING. DESPITE MODERATE INSTABILITY OF 1500-2000 J/KG OF MUCAPE...DEEP LAYER SHEAR REMAINS VERY WEAK...LESS THAN 10 KTS EXPECTED TODAY. THUS...EXPECT A NON-ZERO SEVERE THREAT. THE MAIN THREAT FROM ANY STORM WILL BE LOCALLY HEAVY/SLOW MOVING STORMS OWING TO HIGH PWS OF 1.75-1.8" AND WEAK WIND ALOFT. THE PRESENCE OF WEAK LIFT/FORCING ALOFT COULD SUPPORT ISOLATED SHOWERS INTO THE EARLY MORNING HOURS SATURDAY...MAINLY ACROSS THE WESTERN PIEDMONT AS DRIER AIR ALOFT SPREADS INTO THE AREA FROM THE EAST. EXPECT ONE MORE DAY OF WARM ABOVE-NORMAL TEMPERATURES IN ADVANCE OF THE BACK-DOOR FRONT LATER THIS EVENING. HIGHS IN THE UPPER 80S TO LOWER 90S. NELY LOW-LEVEL FLOW AS SURFACE HIGH PRESSURE RIDGES SOUTH DOWN THE MID-ATLANTIC REGION COULD SUPPORT AREAS STRATUS OVERNIGHT. LOWS IN THE MID 60S TO AROUND 70. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 325 AM FRIDAY... SURFACE HIGH PRESSURE WILL BUILD/EXTEND SOUTHWARD INTO THE REGION ON SATURDAY AND SATURDAY NIGHT... WITH A FAIRLY DEEP NORTHEAST TO EASTERLY FLOW AS THE SURFACE FRONT SETTLES TO THE SOUTH OF CENTRAL NC. THIS SHOULD YIELD A RATHER CLOUDY PERIOD... WITH THE POTENTIAL FOR SOME SCATTERED SHOWERS AND PERHAPS A FEW ISOLATED STORMS AS A WEAK MID LEVEL LOW IS FORECAST TO LINGER JUST TO THE SOUTH OF CENTRAL NC. WILL GO ON THE COOL SIDE OF GUIDANCE GIVEN THE CAD-LIKE SURFACE PATTERN AND CLOUD COVER... WITH HIGH TEMPS SATURDAY EXPECTED TO RANGE FROM THE UPPER 70S NW TO THE MID 80S SE. MORE OF THE SAME IS EXPECTED ON SATURDAY NIGHT... WITH LOW TEMPS BY SUNDAY MORNING IN THE MID TO UPPER 60S. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 325 AM FRIDAY... AT THE BEGINNING OF THE PERIOD...THE UPPER AIR PATTERN WILL FEATURE A WEAK UPPER LEVEL LOW OVER THE SE U.S. COAST AND AN UPPER LEVEL HIGH OVER THE NORTHERN MID ATLANTIC. AT THE SURFACE...A RIDGE OF HIGH PRESSURE WILL ALIGN FAIRLY CLOSE TO THE APPALACHIANS. THIS SET-UP WILL SUPPORT A FAIRLY DEEP E-NE FLOW OVER CENTRAL NC. THIS FETCH ORIGINATES OFF THE ATLANTIC...SO APPEARS THAT WE WILL HAVE A DECENT SUPPLY OF MOISTURE FLOWING INTO OUR AREA. THIS SUGGEST AN ENHANCED POTENTIAL FOR EXTENSIVE CLOUD COVER ON SUNDAY...POSSIBLY CONTINUING INTO MONDAY. MODEL GUIDANCE HAS BEEN FAIRLY CONSISTENT IN ITS DEPICTION OF A WEAK UPPER LEVEL DISTURBANCE MOVING ONSHORE EARLY SUNDAY THEN DRIFTING WEST-SW SUNDAY AFTERNOON-SUNDAY NIGHT. THIS FEATURE INTERACTING WITH AVAILABLE MOISTURE AND MODEST INSTABILITY MAY SUPPORT A FEW SHOWERS AND ISOLATED T-STORMS BY SUNDAY AFTERNOON. AIR MASS TO THE WEST-NW OF RALEIGH MAY BE QUITE STABLE...SO CHARACTER OF PRECIP MAY BE MORE STRATIFORM RATHER THAN SHOWERY. PATTERN CHANGES LITTLE FOR MONDAY THOUGH MAY START TO SEE A SOUTHWESTWARD DRIFT TO THE UPPER LEVEL LOW AND AN EVENTUAL WEAKENING OF THE MOISTURE FEED OFF THE ATLANTIC. ALSO...DIFFICULT TO DISCERN ANY NOTABLE FEATURE ALOFT TO ORGANIZE OR ENHANCE PRECIP ACTIVITY. THUS...EXPECT SHOWER COVERAGE TO BE LESS MONDAY COMPARED TO SUNDAY. AFTERNOON TEMPS SUNDAY AND MONDAY WILL AVERAGE SLIGHTLY BELOW NORMAL. IF CLOUDS/PRECIP MORE EXTENSIVE THAN CURRENT THINKING...MUCH OF THE PIEDMONT WILL STRUGGLE TO REACH 80 DEGREES SUNDAY. MAX TEMPS SUNDAY 80 NW TO LOW-MID 80S EAST-SE...AND LOWER 80S NW TO MID 80S EAST-SE MONDAY. MIN TEMPS IN THE 60S. THE UPPER LEVEL LOW RETROGRADES WEST-SW THROUGH MID WEEK. THIS ALLOWS THE BERMUDA HIGH TO RE-ASSERT ITSELF INTO THE SE U.S. THIS SUGGEST A RETURN TO MORE LATE SUMMER CONDITIONS WITH CONVECTIVE ACTIVITY MAINLY DRIVEN BY DIURNAL HEATING AND AFTERNOON TEMPS 3-6 DEGREES ABOVE NORMAL. EXPECT THE WARMEST/HOTTEST DAYS TO OCCUR WEDNESDAY AND THURSDAY. AN APPROACHING S/W IN THE NORTHERN STREAM MAY BRING AN INCREASED THREAT FOR SHOWERS AND T-STORMS LATE THURSDAY INTO FRIDAY. && .AVIATION /11Z FRIDAY THROUGH TUESDAY/... AS OF 700 AM FRIDAY... 24 HR TAF PERIOD: ANY FOG THAT DEVELOPED THIS MORNING SHOULD LIFT EITHER BEFORE OR SHORTLY AFTER 12Z... WITH SKIES BECOMING MOSTLY SUNNY BY MID MORNING. HOWEVER... AS A MID/UPPER LEVEL DISTURBANCE CONTINUES TO MOVE INTO THE REGION COUPLED WITH THE APPROACH OF A BACKDOOR COLD FRONT... EXPECT CLOUD COVER SHOULD THICKEN THIS AFTERNOON INTO THE EVENING... WITH SCATTERED TO POTENTIALLY NUMEROUS SHOWERS AND STORMS DEVELOPING. THUS... HAVE ADDED A PROB30 GROUP FOR THE POTENTIAL FOR CONVECTION THIS AFTERNOON AND EVENING AT ALL TAF SITES. ANY STORMS THAT DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE AT LEAST IFR CONDITIONS IN HEAVY RAIN... ALONG WITH GUSTY WINDS. LOW STRATUS AND/OR FOG MAY DEVELOP NEAR THE IN OF THE TAF PERIOD. HOWEVER... CONFIDENCE IS RATHER LOW THIS FAR OUT (WITH MIXED SIGNALS IN THE GUIDANCE). THUS.. WILL JUST ADD A TEMPO FOR MVFR STRATUS TO SHOW THE POTENTIAL FOR SUB-VFR CONDITIONS. OUTLOOK: MORE WIDELY SCATTERED CONVECTION IS POSSIBLE DURING THE AFTERNOON AND EVENING ON SATURDAY AND SUNDAY WITH A DECREASE IN COVERAGE AND A FOCUS TOWARD THE COASTAL PLAIN ON MONDAY AND TUESDAY. LATE NIGHT AND MORNING FOG AND STRATUS WITH POTENTIALLY SIGNIFICANT RESTRICTIONS APPEAR PROBABLE ON SATURDAY AND SUNDAY MORNINGS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BSD/26 NEAR TERM...CBL SHORT TERM...BSD LONG TERM...WSS AVIATION...BSD/BLAES

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